Search

Effective control of shale swelling and lost circulation using drilling fluid is considered the dominant strategy for maintaining borehole stability, especially drilling operations in deep oil and gas wells. In this work, a hybrid silicate that contains lithium silicate and potassium methyl silicate (PMS) was employed as a film-forming additive to reduce shale hydration and filtration loss in the high-temperature drilling fluid. Scanning electron microscopy (SEM) results revealed that a dense quartz crystal film coating on the shale can be formed in a hybrid silicate solution when the temperature exceeds 150 °C. The in situ-formed film on the shale surface with a thickness of 60-130 μm was composed of fibrous crystalline silica. Furthermore, the aqueous hybrid silicate exhibited enhanced hydration inhibition ability by preventing water invasion of the formation. Aqueous hybrid silicate with a concentration of 0.5-3 wt % lithium silicate and 0.1-0.2 mol/L PMS was first chosen to obtain the optimum concentration according to the hydration inhibition ability and film formation characteristics. The hybrid silicate was added into a drilling fluid formulation applicable in high-pressure and high-temperature conditions, and the rheological characteristics and filtration properties were investigated. The results confirmed that drilling fluids with the addition of hybrid silicate can mitigate variation of viscosity and yield point before and after aging at 180 and 220 °C. Besides, the filtration behavior was also improved by adding hybrid silicate into the drilling fluid. A lower filtration loss was observed at the concentration of 1.0 wt % lithium silicate and 0.2 mol/L potassium methyl silicate, which showed 63 and 50% HPHT fluid loss reduction for unweighted and weighted formulations at 205 °C and 3.5 MPa, respectively. In addition, the drilling fluid featured stable rheological and filtration properties and excellent shale hydration inhibition characteristics when exposed to high temperatures, making it a promising candidate for drilling in deep oil and gas wells.

The Xiagou Formation is the main tight oil reservoir in Qingxi Sag of Jiuquan Basin. Given the poor physical properties and other factors restricting tight oil exploitation and production in this area, studies should focus on microscopic pore structure characteristics. In this study, a nano-CT scanner, a SEM, and an NMR were used to study the pore structure characteristics of a tight carbonate reservoir in Qingxi Sag, Jiuquan Basin. The Xiagou Formation reservoir mainly consists of gray argillaceous dolomite and dolomitic mudstone. The pore categories are mainly elliptic, irregular, intergranular, and intragranular and mostly filled with clay and carbonate cement. Pore space is small, the intergranular or organic pores are mostly separated, and pore-throat is weakly connected. The throats mostly develop with lamellar and tube bundle-like characteristics and with poor seepage ability. The pore-throats mostly span from nanometer to micrometer sizes, and pore diameters are mainly concentrated in the range of 0.01–0.1 and 1–10 μm. It is a unimodal pattern mainly composed of micropores, or a bimodal regular allocation dominated by micropores supplemented by macropores. The relationship between micropore (1 μm) content allocation and mean pore diameter strongly controls the permeability of reservoir rocks. When macropore content reaches more than 85%, or when pore content totals less than 3%, the permeability of a reservoir remarkably increases. At a higher ratio of the average finest throat sectional area and throat-pore of reservoir rock, the throat radius lies closer to the connecting pore radius, pore and throat connectivity improves, and reservoir seepage ability becomes stronger. Based on reservoir capacity and seepage ability, pore structures of the tight carbonate reservoirs in study area are classified into type I (small-pore–thin-throat), type II (thin-pore–thin-throat), and type III (microporous-microthroat) with rock permeability>0.1 mD, 0.05–0.1 mD, and

To overcome the negative impact on the rheological and filtration loss properties of drilling fluids caused by elevated temperature and salts contamination, which are common in ultradeep or geothermal drilling operations, it is imperative to develop highly efficient additives used in the water-based drilling fluid. In this study, a zwitterionic copolymer P (AM/DMC/AMPS/DMAM, ADAD) was synthesized by using acrylamide (AM), cationic monomer methacrylatoethyl trimethyl ammonium chloride (DMC), anionic monomer 2-acrylamide-2-methyl propane sulfonic acid (AMPS), and N,N-dimethylacrylamide (DMAM) through free radical copolymerization. The copolymer was characterized by 1H Nuclear Magnetic Resonance (NMR), Fourier transform infrared spectroscopy (FTIR), elemental analysis, thermogravimetric analysis (TGA), and zeta potential. The rheological behavior, filtration properties, and the performance exposure to salt or calcium contamination in water-based drilling fluid were investigated. The bentonite/polymer suspension showed improved rheological and filtration properties even after aging at 160 °C or a high concentration of salt and calcium. The filtration loss can be greatly reduced by more than 50% (from 18 mL to 7 mL) by the inclusion of 2.0 wt% copolymer, while a slight increase in the filtrate loss was observed even when exposed to electrolyte contamination. Particle size distribution and zeta potential further validate the idea that zwitterionic copolymer can greatly improve the stability of base fluid suspension through positive group enhanced anchoring on the clay surface and repulsion force between negative particles. Moreover, this study can be directed towards the design and application of zwitterionic copolymer in a water-based drilling fluid.

Compared with the overpressure conditions of shale reservoirs in the Jiaoshiba area, exploring the controlling factors of changes in shale reservoir physical properties under normal-pressure accumulation is of great significance to shale gas exploration. To achieve this, X-ray powder diffraction, nitrogen adsorption, and scanning electron microscopy were carried out to determine mineral content, permeability, porosity, and pore structure for well core and outcrop samples of the Wufeng–Longmaxi Formation in southeastern Chongqing, China. Field observations and drilling cores revealed abundant structural fractures in southeastern Chongqing, offering potential main storage space for shale gas. Findings also determined that high-quality source rocks are located in the lower part of the Wufeng–Longmaxi Formation, which features low porosity and low permeability, yet existing structural fractures could potentially improve permeability to a certain extent. The main factors controlling the shale reservoir with the above characteristics include the depositional environment, mineral components, total organic carbon content, and tectonic movement. The deep-water anoxic depositional environment was conducive to the complete preservation of organic matter and sedimentation of the biogenic siliceous minerals, which had a strong effect on improving the porosity of organic matter and brittleness of the rocks. The high content of quartz was found to improve rock compression resistance and brittleness, and increasing clay proportion was found to enhance the interlayer pores of clay minerals. Total organic carbon content, specific surface area, pore volume, and fracture development were all found to have direct contributions to shale gas entrapment. Overall, the most important factor resulting in normal-pressure accumulation in southeastern Chongqing was the intense tectonic movements since the Late Jurassic period which destroyed the original overpressure accumulation conditions.

This study investigates natural tectonic fractures in 22 wells that penetrated the tight oil reservoirs in the middle Permian Lucaogou Formation in the southeastern Junggar Basin, China. Analysis was conducted using conventional image logs of wellbores, acoustic emissions (AEs) data collected from core rock mechanics testing, fluid inclusion analysis, and C–O stable isotopes and Ir element analyses of fracture-filling minerals, in order to constrain the relative timing of fracture development. The geochemical properties of fracture-filling minerals and Kaiser effect points, combined with the regional tectonic analysis, revealed a four-stage fracture development in the tested tight reservoirs. During Stage 1, continuous N–S compression occurred at the end of Late Triassic, producing many NW-trending extensional fractures. Calcite fillings were formed within these fractures at temperatures between 31.7 and 45.0 °C based on fluid inclusion analysis. SW–NE compressive stress was produced in the Middle−Late Jurassic during Stage 2, forming ENE-trending shear fractures. The calcite fillings within these fractures formed at temperatures between 50.1 and 64.6 °C. During Stage 3, intense N–S compression formed NNW-trending shear fractures in the Early Cretaceous, and calcite fillings formed at temperatures between 80.0 and 89.9 °C. Finally, Stage 4 corresponds to nearly N–S compression due to the tectonic activities occurring from Tertiary to nowadays, creating NNW-trending shear fractures; no or minimal partial filling of calcite occurred during this Stage. Based on the relation between the oil generation windows and stages of fracture development, it is proposed that the fractures that developed within the Lucaogou Formation during Stages 2–4 have minimal mineral filling, which is most favorable for oil and gas migration and accumulation.

Deeply buried (3000–5000 m), deltaic sandstones of the Upper Triassic Xujiahe Formation are important tight gas reservoirs in the Sichuan Foreland Basin, China. The diagenesis of these tight sandstones was examined using a variety of petrographic and geochemical techniques, including thin section description, X-ray diffraction (XRD), whole-rock chemical analysis, scanning electron microscopy (SEM), Cathodoluminescence (CL) imaging, electron probe analysis, fluid inclusions and isotopic analysis. These integrated petrographic and geochemical techniques were used to determine the diagenetic history of the sandstones and its impact on the reservoir quality. The tight deltaic sandstones of the T3x2 and T3x4 (second and fourth members of Xujiahe Formation) have undergone a significant and complicated series of diagenetic alterations and changes in geochemical composition. Strong mechanical and chemical compaction together with carbonate cementation destroyed almost all the primary pores and the secondary dissolution pores now dominate the pore space. The T3x4 sandstones experienced a more open diagenetic system at near-surface and eodiagensis resulted in higher porosity than seen in the T3x2 sandstones. Both the T3x2 and T3x4 sandstones experienced closed-system diagenesis during middle-late mesodiagenesis. The early diagenetic dissolution, which mainly occurred in the open geochemical system, produced secondary pores and provided kaolinite and some K+ needed for the subsequent illitization of kaolinite and K-feldspar. The late dissolution of K-feldspar and illitization of K-feldspar in T3x4 sandstones and T3x2 sandstones during the mesodiagenesis, produced some effective secondary pores in the closed geochemical system or in the focused fluid flow zone along fractures. The diagenetic characteristics, size and evolution of (open vs closed) diagenetic system, which were constrained by the depositional environment, deep burial depth and tectonic activity, can be used to predict the reservoir quality ahead of drilling.

China shale oil, which is preserved in lacustrine shale with strong heterogeneity and relatively low maturity, has been a research hotspot of unconventional resources. However, controlling factors of shale oil enrichment and resource potential evaluation restricted efficient exploration and development of lacustrine shale oil. On the basis of well logging data, TOC content, Rock-Eval pyrolysis values, thermal maturity, 100 oil saturation data, and pressure coefficient, the core observation, X-ray diffraction analysis, physical property analysis, scanning electron microscopy, CT scan, well logging interpretation, and volumetric genesis method depending on three-dimensional geological modeling were used to determine enrichment factors and evaluate the resource potential of Qingshankou Formation shale oil in the Southern Songliao Basin. Shale oil was mainly enriched in the semideep and deep lake shale of K2qn1, with the high capacity of hydrocarbon generation and favorable petrological and mineralogical characteristics, pore space characteristics, and physical properties in the low structural part of the Southern Songliao Basin. The three-dimensional geological resource model of Qingshankou Formation lacustrine shale oil was determined by the key parameters (Ro, TOC, and ) of shale oil in the favorable zone of the Southern Songliao Basin, northeast China. The geological resource of shale oil, which was calculated by two grid computing methods ( and ), was, respectively, and . The great shale oil resource indicates a promising future in the exploration and development of Qingshankou Formation shale oil of the Southern Songliao Basin.

Two oolites of the Lower Triassic Feixianguan Formation on the margins of the Kaijiang-Liangping (K-L) Trough in the NE Sichuan Basin were deposited in the upper parts of similar shallowing-upward sequences, and are capped by a subaerial exposure surface. However, they have contrasting diagenetic histories and reservoir qualities: the sour oolitic dolostone reservoirs on the eastern side of the K-L Trough have significantly higher porosities than the sweet oolitic limestone reservoirs on the western side. A petrologic and geochemical comparison of the two oolites was carried out so as to investigate the role of diagenetic processes on the co-evolution of oolite structure and pore network. On both sides of the K-L Trough, eogenetic meteoric digenesis led to an inversion of texture with ooid dissolution and interparticle cementation in the oolite layers close to the exposure surface. The layers relatively far from the exposure surface mostly underwent recrystallization in association with connate seawater, resulting in neomorphic fabrics in the ooid cortices and less interparticle calcite cement. During the subsequent dolomitization, the early-formed oolite structure were mostly inherited by the dolostones on the eastern side, with fabric-retentive textures in the layers close to the exposure surface and fabric-destructive textures in the layers far from the exposure surface. During deeper burial the oolitic limestones were subjected to extensive calcite cementation and porosity loss, whereas the dolostones generally retained more porosity and have better connectivity of the micropore network. The higher porosity of the dolostones is ascribed to lesser chemical compaction and associated cement precipitation, rather than the creation of new pores. Porosity enhancement is closely dependent on the absence of the calcite cement related to pressure solution. The heterogeneity of the dolostone fabrics and the porosity was further enhanced by the subsequent recrystallization and the dissolution-reprecipitation process induced by thermochemical sulfate reduction, during which small amounts of net porosity are calculated to have been created. The oolitic limestones are the best reservoirs close to the exposure surface, whereas the most porous dolostones with the highest degree of fabric destruction are commonly some distance from the exposure surface. These results provide some insights into the diagenetic controls on oolite structure and porosity, and have implications for predicting the porosity of deeply-buried oolitic reservoirs, so have global theoretical and practical significance.

Previous studies have reported faunal changeover and carbon isotope excursions through the Wuchiapingian–Changhsingian (W C) transition, a geologically significant period of time that bridged two major extinction events: the end-Permian and Guadalupian–Lopingian boundary mass extinctions. However, the causes of the carbon isotope excursion across the W C interval remain poorly understood. This study presents sedimentological and geochemical data from three well-exposed sections in the lower Yangtze region, South China. A strong negative carbon isotope excursion in organic matter is recorded across the W C interval and correlates well with other sections in South China. Sedimentology and elemental geochemistry indicate that the lower Yangtze region experienced a distinct regional deepening during the W C transition inducing bottom water redox changes increased primary productivity. Possible causes of the negative carbon isotope excursion at the W C boundary include selective preservation of organic matter during early diagenesis under anoxic/euxinic conditions and changes in terrigenous organic matter input. Both of these factors were controlled by regional relative sea-level rise triggered by contemporaneous tectonic movements.

Objective: To evaluate the characteristics of force degradation of latex elastics in clinical applications and in vitro studies. Materials and Methods: Samples of 3/16-inch latex elastics were investigated, and 12 students between the ages of 12 and 15 years were selected for the intermaxillary and intramaxillary tractions. The elastics in the control groups were set in artificial saliva and dry room conditions and were stretched 20 mm. The repeated-measure two-way analysis of variance and nonlinear regression analysis were used to identify statistical significance. Results: Overall, there were statistically significant differences between the different methods and observation intervals. At 24- and 48-hour time intervals, the force decreased during in vivo testing and in artificial saliva (P < .001), whereas there were no significant differences in dry room conditions (P > .05). In intermaxillary traction the percentage of initial force remaining after 48 hours was 61%. In intramaxillary traction and in artificial saliva the percentage of initial force remaining was 71%, and in room conditions 86% of initial force remained. Force degradation of latex elastics was different according to their environmental conditions. There was significantly more force degradation in intermaxillary traction than in intramaxillary traction. The dry room condition caused the least force loss. Conclusions: There were some differences among groups in the different times to start wearing elastics in intermaxillary traction but no significant differences in intramaxillary traction.

To improve the corrosion resistance of N80steel, Ni-W-P coating was prepared by electroless deposition. The corrosion properties for Ni-W-P coating were investigated in hypersaline ground brine. Results of weight loss tests show that the corrosion resistance of the Ni-W-P coating is 10 times of N80steel in hypersaline brine at 90 °C. Electrochemical tests show that the current density of Ni-WP coated sample reduce from 7.94×10 μA/cm to 4.28×10 μA/cm, and the corrosion potential changes from –0.700 V to –0.398 V compared with N80steel. Scanning electron microscopy (SEM) micrographs and X-ray photoelectron spectroscopy (XPS) were used to evaluate the morphology and composition of the corrosion layer of Ni-W-P coating. The results show that severe intergranular corrosion appear in N80steel, whereas no intergranular corrosion occur in NiW-P coating. The chemical composition of the corrosion layer of Ni-W-P coating is NiO,WO3, phosphate, and hypophosphite which led to superior corrosion resistance in hypersaline brine. This study confirms that the Ni-W-P coating can be applied for corrosion protection in hypersaline environment. Keywords-Ni-W-P coating; hypersaline brine; corrosion; corrosion resistance;corrosion layer